Networking Concept

A very important diagram to remember that will certainly help you in a lot of interview questions

Networks consist of hosts i.e. members, usually computers but possibly other participating devices such as printers. A collection of hosts on a network is sometimes referred to as a site. All hosts on a network, as well as being connected by some medium either wired or wireless, must also agree on a set of protocols for communicating with each other. The OSI model is an abstract reference model for communications and computer network protocol design. 

The internet protocol suite commonly used on the internet roughly maps to the OSI model as shown in the diagram.

The everyday protocols you use are at the top (application layer). Examples include ssh (for
connecting to machines), ftp (for transferring files), http (for browsing the web) and smtp (for
sending email).

Underneath these applications, either TCP or UDP is used to actually transport data packets. Transmissions Control Protocol (TCP) is a connection-oriented protocol that offers guaranteed delivery of packets (with an overhead in network handshaking that this requires) while User Datagram Protocol (UDP) is a connectionless protocol that transmits packets on a best effort basis without any guarantees about delivery.

TCP and UDP run on the Internet Protocol which describes the protocol used to encapsulate and transport data around the network. It handles details such as addressing and routing. Dynamic routing of IP packets around the network is handled by protocols including RIP, BGP and OSPF. 

Internet Control Message Protocol (ICMP) is used to send status and error messages around IP networks (this is the protocol used by tools such as ping).

At the lowest level, the Address Resolution Protocol (ARP) is used to map IP addresses back to the physical addresses used by the underlying hardware. In the case of Ethernet networks for instance, each network device has a unique physical address (the MAC address). ARP is used to map these addresses to the IP addresses used at the logical network level.

The internet protocol suite can run on a variety of physical networks and media including Ethernet, Token Ring and Wireless..